The present invention relates generally to the field of underground boring and, more particularly, to a closed-loop control system and process which employs an inertial navigation sensor package for controlling an underground boring machine in real-time.
Utility lines for water, electricity, gas, telephone and cable television are often run underground for reasons of safety and aesthetics. In many situations, the underground utilities can be buried in a trench which is then back-filled. Although useful in areas of new construction, the burial of utilities in a trench has certain disadvantages. In areas supporting existing construction, a trench can cause serious disturbance to structures or roadways. Further, there is a high probability that digging a trench may damage previously buried utilities, and that structures or roadways disturbed by digging the trench are rarely restored to their original condition. Also, an open trench poses a danger of injury to workers and passersby.
The general technique of boring a horizontal underground hole has recently been developed in order to overcome the disadvantages described above, as well as others unaddressed when employing conventional trenching techniques. In accordance with such a general horizontal boring technique, also known as microtunnelling, horizontal directional drilling (HDD) or trenchless underground boring, a boring system is situated on the ground surface and drills a hole into the ground at an oblique angle with respect to the ground surface. Drilling fluid is typically flowed through the drill string, over the boring tool, and back up the borehole in order to remove cuttings and dirt. After the boring tool reaches a desired depth, the tool is then directed along a substantially horizontal path to create a horizontal borehole. After the desired length of borehole has been obtained, the tool is then directed upwards to break through to the surface. A reamer is then attached to the drill string which is pulled back through the borehole, thus reaming out the borehole to a larger diameter. It is common to attach a utility line or other conduit to the reaming tool so that it is dragged through the borehole along with the reamer.
In order to provide for the location of a boring tool while underground, a conventional approach involves the incorporation of an active sonde disposed within the boring tool, typically in the form of a magnetic field generating apparatus that generates a magnetic field. A receiver is typically placed above the ground surface to detect the presence of the magnetic field emanating from the boring tool. The receiver is typically incorporated into a hand-held scanning apparatus, not unlike a metal detector, which is often referred to as a locator. The boring tool is typically advanced by a single drill rod length after which boring activity is temporarily halted. An operator then scans an area above the boring tool with the locator in an attempt to detect the magnetic field produced by the active sonde situated within the boring tool. The boring operation remains halted for a period of time during which the boring tool data is obtained and evaluated. The operator carrying the locator typically provides the operator of the boring machine with verbal instructions in order to maintain the boring tool on the intended course.
It can be appreciated that present methods of detecting and controlling boring tool movement along a desired underground path is cumbersome, fraught with inaccuracies, and require repeated halting of boring operations. Moreover, the inherent delay resulting from verbal communication of course change instructions between the operator of the locator and the boring machine operator may compromise tunneling accuracies and safety of the tunneling effort. By way of example, it is often difficult to detect the presence of buried objects and utilities before and during tunneling operations. In general, conventional boring systems are unable to quickly respond to needed boring tool direction changes and productivity adjustments, which are often needed when a buried obstruction is detected or changing soil conditions are encountered.
Another conventional approach to detecting the location of a drill bit used in vertical oil or gas well drilling applications involves the use of a down-hole gyroscope-based surveying tool. Examples of such an approach are disclosed in U.S. Pat. Nos. 5,652,617; 5,394,950; 4,987,684; 4,909336; 4,739,841; 4,454,756; 4,302,886; 4,297,790; 4,071,959; 4,021,774; and 3,845,569; all of which are hereby incorporated herein by reference in their respective entireties. These and other conventional approaches are specifically designed for use in vertically oriented wells (e.g., along a relatively fixed vertical axis).
Moreover, such conventional down-hole gyroscope-based surveying tools are generally used to facilitate maintaining of drill bit progress in the vertical direction. Also, many of the systems disclosed in the above-listed patents are employed to survey a previously excavated vertical well. Further, use of such a conventional gyroscope-based surveying tool requires a skilled operator to interpret the information produced by the surveying tool, manually determine an appropriate course of action upon interpreting the information, and, finally, initiating an appropriate change to the vertical drilling rig operation by use of one or more user actuated controls. It can be appreciated that these operations require the presence of a relatively highly skilled operator at the vertical drilling rig. It can be further appreciated that the human factor associated with such approaches results in a relatively slow response time to changing well conditions and reduced surveying accuracies.
During conventional horizontal and vertical drilling system operations, as discussed above, the skilled operator is relied upon to interpret data gathered by various down-hole information sensors, modify appropriate controls in view of acquired down-hole data, and cooperate with other operators typically using verbal communication in order to accomplish a given drilling task both safely and productively. In this regard, such conventional drilling systems employ an "open-loop" control scheme by which the communication of information concerning the status of the drill head and the conversion of such drill head status information to drilling machine control signals for effecting desired changes in drilling activities requires the presence and intervention of an operator at several points within the control loop. Such dependency on human intervention within the control loop of a drilling system generally decreases overall excavation productivity, increases the delay time to effect necessary changes in drilling system activity in response to acquired drilling machine and drill head sensor information, and increases the risk of injury to operators and the likelihood of operator error.
There exists a need in the excavation industry for an apparatus and methodology for controlling an underground boring tool and boring machine with greater responsiveness and accuracy than is currently attainable given the present state of the technology. There exists a further need for such an apparatus and methodology that may be employed in vertical and horizontal drilling applications. The present invention fulfills these and other needs.